scholarly journals Broadband RCS Reduction by a Quaternionic Metasurface

Materials ◽  
2021 ◽  
Vol 14 (11) ◽  
pp. 2787
Author(s):  
Zhao Zhang ◽  
Yazhong Zhang ◽  
Tianlong Wu ◽  
Shaowen Chen ◽  
Wei Li ◽  
...  
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Cross Section ◽  
Phase Difference ◽  
Software Package ◽  
Superposition Principle ◽  
Analytical Calculation ◽  
Scattering Mechanism ◽  
Angular Performance ◽  
Commercial Software Package

A quaternionic metasurface consisting of two pairs of units with destructive phase difference is proposed to extend the bandwidth of radar cross section (RCS) reduction. The two pairs of units are designed to have complementary phase-different bandwidth, which extends the bandwidth of RCS reduction. The overlaps of their bandwidth enhance the RCS reduction, resulting in a metasurface having broadband and strong RCS reduction. This design and the wideband RCS reduction of the quaternionic metasurface were verified by analytical calculation with superposition principle of electric field, numerical simulation with commercial software package CST Microwave Studio and experiment in microwave anechoic chamber. The scattering mechanism and the angular performance of the quaternionic metasurface were also investigated.

Numerical Simulation of Inhomogeneous Food with Ohmic heating

2010 ◽  
Vol 6 (4) ◽  
Author(s):  
Xin Jiang ◽  
Lin Li ◽  
Wuxiong Shen ◽  
Jiahua Zhou
Keyword(s):  
Numerical Simulation ◽  
Finite Element Method ◽  
Electrical Conductivity ◽  
Electric Field ◽  
Electric Conductivity ◽  
Cross Section ◽  
Thermal Processing ◽  
Food System ◽  
Ohmic Heating ◽  
Processing Technique

Ohmic heating is an emerging thermal processing technique in which electrical conductivity is one of the most important factors. Inhomogeneous cuboid food models were built with a plate inserted in the center of a food system. The effects of the plate’s electric conductivity on both the surrounding material (?p/?s) and the orientation of the plate in ohmic heating were analyzed with a finite element method. It was revealed that when the plate’s electric conductivity was lower than that of the surrounding material, the plate’s temperature was lower than the surrounding material when the biggest cross-section of the plate was parallel to the electric field. When the biggest cross-section of the plate was perpendicular to electric field, the case was more complicated. The plate’s temperature was higher than that of the surrounding material when ?p/?s was 0.1 and 0.5. The plate’s temperature was lower than that of the surrounding material when ?p/?s was 0 and 0.02. When the plate’s electric conductivity was higher than that of the surrounding material, the plate’s temperature was always lower than that of the surrounding material when the biggest cross-section of the plate was perpendicular to the electric field. When the biggest cross-section of plate was parallel to that of the electric field, the case was more complicated. The plate’s temperature was higher than that of the surrounding material when ?p/?s was 2 and 10. The plate’s temperature was lower than that of the surrounding material when ?p/?s was 50.

scholarly journals Engineering methods for calculation of elements from combined glued timber

2020 ◽  
Vol 11 (2) ◽  
pp. 79-90
Author(s):  
S. I. Bilyk ◽  
D. V. Mykhaіlovskyi
Keyword(s):  
Finite Element ◽  
Cross Section ◽  
Software Package ◽  
Strength Class ◽  
Rectangular Cross Section ◽  
Analytical Calculation ◽  
The Finite Element Method ◽  
Cross Sectional ◽  
Numerical Studies ◽  
Reduced Modulus

Extensive world experience in the implementation of building structures made of timber, in particular glued timber, for various purposes confirms the feasibility of their use. This is facilitated by the fact that glued timber effectively accumulates the positive properties of timber as a structural material level the shortcomings of solid timber. One of the types of constructions of glued timber are constructions of combined glued timber. Taking into account the structure and features of elements of combined glued timber of rectangular cross section, for a detailed analysis of the stress-strain state, a method is proposed, which consists in applying to standard formulas for calculating the reduced cross-sectional characteristics: reduced area, reduced moment of inertia, reduced moment of resistance. To calculation, the elements of combined glued timber of rectangular cross section according to the second limit state (serviceability), it is proposed to use the reduced modulus of elasticity of the section to the boards of the outer layers. To analyze the proposed method, a number of numerical studies of beams of combined and glued timber of the same strength class using analytical calculation methods and using the finite element method in the software package LIRA-CAD, using three-dimensional and flat finite elements. Numerical studies show that the results of calculations of beams of combined glued and glued timber of the same strength class differ within 20% in the direction of increasing the values of deflections and normal stresses in the elements of combined glued timber. Finite element calculations in the software package LIRA-CAD beams of combined and glued timber of the same strength class modeled volumetric and flat showed almost complete coincidence of results with a discrepancy of up to 2%, which suggests the need to significantly simplify the modeling, set elements from glued timber with flat finite elements. It is confirmed that the analytical calculation of beams of combined glued timber is recommended to be carried out according to the proposed method. The proposed technique allows to take into account the thickness and mechanical characteristics for the strength class of each board of which the glued cross section of the element, which significantly expands the range of use of combined glued timber. The high level of coincidence (within 5%) of the proposed analytical method with determination of the given cross-sectional characteristics with the results obtained by the finite element method for different cross-sections and spans of beams is confirmed, which allows to assert the expediency of its application in engineering calculations. In addition, the modeling of structures made of combined glued timber is possible with rod elements with the provision of the reduced modulus of elasticity according to the proposed method, which greatly simplifies the calculation of complex rod systems.

scholarly journals Calculation of wave conditions in water area with sharp bottom unevenness

2018 ◽  
Vol 251 ◽  
pp. 04048
Author(s):  
Igor Kantarzhi ◽  
Alexander Gogin
Keyword(s):  
Numerical Simulation ◽  
Numerical Modeling ◽  
Software Package ◽  
Analytical Calculation ◽  
Water Area ◽  
Building Codes ◽  
Hydraulic Structures ◽  
Bottom Relief ◽  
Wave Conditions ◽  
Definition Of

Design of marine hydraulic structures is associated with definition of design wave conditions close by these structures. Safety and economy of hydraulic structures depend exactly on characteristics of wave conditions. In this paper, we consider two methods of obtaining the design wave: analytical calculation using Building Codes and Regulations of Russia and numerical modeling. The MIKE 21 software package was used in this case to perform the numerical simulation. A feature of the considered area is the unevenness of the bottom relief of the water area. The purpose of the article is to show clearly, how much characteristics of the design wave can be overstated when calculating in according to the normative document that does not take into account features of the water area.

Composite right/left-handed transmission line with array of thermocouples for generating terahertz radiation

2020 ◽  
Vol 92 (2) ◽  
pp. 20502
Author(s):  
Behrokh Beiranvand ◽  
Alexander S. Sobolev ◽  
Anton V. Kudryashov
Keyword(s):  
Transmission Line ◽  
Terahertz Radiation ◽  
Transmission Lines ◽  
Software Package ◽  
Optical Pulses ◽  
Capacitively Coupled ◽  
Voltage Difference ◽  
Left Handed ◽  
Microwave Transmission ◽  
Commercial Software Package

We present a new concept of the thermoelectric structure that generates microwave and terahertz signals when illuminated by femtosecond optical pulses. The structure consists of a series array of capacitively coupled thermocouples. The array acts as a hybrid type microwave transmission line with anomalous dispersion and phase velocity higher than the velocity of light. This allows for adding up the responces from all the thermocouples in phase. The array is easily integrable with microstrip transmission lines. Dispersion curves obtained from both the lumped network scheme and numerical simulations are presented. The connection of the thermocouples is a composite right/left-handed transmission line, which can receive terahertz radiation from the transmission line ports. The radiation of the photon to the surface of the thermocouple structure causes a voltage difference with the bandwidth of terahertz. We examined a lossy composite right/left-handed transmission line to extract the circuit elements. The calculated properties of the design are extracted by employing commercial software package CST STUDIO SUITE.

Numerical Simulation of Leakage Current on Conductive Insulator Surface

2019 ◽  
Vol 8 (4) ◽  
pp. 9487-9492
Keyword(s):  
Numerical Simulation ◽  
Electric Field ◽  
Leakage Current ◽  
Method Of Lines ◽  
Electron Attachment ◽  
Negative Ions ◽  
Conduction Current ◽  
Insulator Surface ◽  
Finite Difference Approximations ◽  
Positive Ions

The outdoor insulator is commonly exposed to environmental pollution. The presence of water like raindrops and dew on the contaminant surface can lead to surface degradation due to leakage current. However, the physical process of this phenomenon is not well understood. Hence, in this study we develop a mathematical model of leakage current on the outdoor insulator surface using the Nernst Planck theory which accounts for the charge transport between the electrodes (negative and positive electrode) and charge generation mechanism. Meanwhile the electric field obeys Poisson’s equation. Method of Lines technique is used to solve the model numerically in which it converts the PDE into a system of ODEs by Finite Difference Approximations. The numerical simulation compares reasonably well with the experimental conduction current. The findings from the simulation shows that the conduction current is affected by the electric field distribution and charge concentration. The rise of the conduction current is due to the distribution of positive ion while the dominancy of electron attachment with neutral molecule and recombination with positive ions has caused a significant reduction of electron and increment of negative ions.

Numerical Simulation of the Effects of Preheating on Electron Beam Additive Manufactured Ti-6Al-4V Build Plate

2016 ◽  
Vol 879 ◽  
pp. 274-278 ◽  
Author(s):  
Jun Cao ◽  
Philip Nash
Keyword(s):  
Numerical Simulation ◽  
Residual Stress ◽  
Finite Element ◽  
Electron Beam ◽  
Cross Section ◽  
Element Model ◽  
Normal Direction ◽  
Thermal Residual Stresses ◽  
Longitudinal Residual Stress ◽  
Middle Cross Section

In an earlier study, a 3-D thermomechanical coupled finite element model was built and experimentally validated to investigate the evolution of the thermal residual stresses and distortions in electron beam additive manufactured Ti-6Al-4V build plates. In this study, an investigation using this robust and accurate model was focused on an efficient preheating method, in which the electron beam quickly scanned across the substrate to preheat the build plate prior to the deposition. Various preheat times, beam powers, scan rates, scanning paths and cooling times (between the end of current preheat scan/deposition layer and the beginning of the next preheat scan/deposition layer) were examined, and the maximum distortion along the centerline of the substrate and the maximum longitudinal residual stress along the normal direction on the middle cross-section of the build plate were quantitatively compared. The results show that increasing preheat times and beam powers could effectively reduce both distortion and residual stress for multiple layers/passes components.

Sign in / Sign up

Export Citation Format

Share Document